Criteria for Comparison of Phosgenation Reagents

Yield is still the primary criterion in chemistry because, indirectly, it contains some other preparative criteria such as reactivity and selectivity, and also has a significant bearing on costs. Therefore, yield will be the leading criterion in our comparison of same and similar reactions accomplished with various phosgenation reagents. Further criteria to be taken into consideration are purity, handling, and work-up, as well as safety, toxicity, and environmental impact. 

For chlorocarbonylations, only phosgene, diphosgene, and triphosgene are able to 

Benzyl alcohol does not react with triphosgene at the low temperatures used in the above example in the absence of a base. On reacting benzyl alcohol with triphosgene at room temperature in the presence of pyridine, only benzyl chloride is isolated. Chloroformate 1 is formed initially, and if the alcohol is activated, as in the case of benzyl alcohol, decomposition ensues under these conditions, generating benzyl chloride in 90% yield [5]. (If the alcohol is not activated, decomposition will not occur.) Optimizations aimed at achieving higher yields of chloroformate 1 from the reaction of benzyl alcohol with triphosgene without a base led to a maximum of 15% of 1 besides 2 [4]. 

Comparing the formation of chloroformate 3 with triphosgene and of oxycarbonyl imidazole 4 with GDI, respectively, as activated intermediates for the preparation of carbamates at 7-0-taxol shows that, under similar reaction conditions, CDI yields better results than triphosgene [6] (see Section 4.2.1). 

Reaction of 2 -0-R-taxol with triphosgene requires a six-fold excess of the reagent and at least a nine-fold excess of base providing a 60-70% yield of 3, which is 

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